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General clean-up of the bitcode format documentation. Having the paragraphs

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formatted the same, putting words in <tt> tags, adding &mdash;s, etc.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@68426 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bill Wendling
2009-04-04 22:27:03 +00:00
parent cfdd807cfa
commit bb7425fafb
1 changed files with 206 additions and 149 deletions
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docs/BitCodeFormat.html
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@@ -180,13 +180,15 @@ value of 24 (011 << 3) with no continuation. The sum (3+24) yields the value
<p>6-bit characters encode common characters into a fixed 6-bit field. They <p>6-bit characters encode common characters into a fixed 6-bit field. They
represent the following characters with the following 6-bit values:</p> represent the following characters with the following 6-bit values:</p>
<ul> <div class="doc_code">
<li>'a' .. 'z' - 0 .. 25</li> <pre>
<li>'A' .. 'Z' - 26 .. 51</li> 'a' .. 'z' &mdash; 0 .. 25
<li>'0' .. '9' - 52 .. 61</li> 'A' .. 'Z' &mdash; 26 .. 51
<li>'.' - 62</li> '0' .. '9' &mdash; 52 .. 61
<li>'_' - 63</li> '.' &mdash; 62
</ul> '_' &mdash; 63
</pre>
</div>
<p>This encoding is only suitable for encoding characters and strings that <p>This encoding is only suitable for encoding characters and strings that
consist only of the above characters. It is completely incapable of encoding consist only of the above characters. It is completely incapable of encoding
@@ -226,14 +228,14 @@ The set of builtin abbrev IDs is:
</p> </p>
<ul> <ul>
<li>0 - <a href="#END_BLOCK">END_BLOCK</a> - This abbrev ID marks the end of the <li><tt>0 - <a href="#END_BLOCK">END_BLOCK</a></tt> &mdash; This abbrev ID marks
current block.</li> the end of the current block.</li>
<li>1 - <a href="#ENTER_SUBBLOCK">ENTER_SUBBLOCK</a> - This abbrev ID marks the <li><tt>1 - <a href="#ENTER_SUBBLOCK">ENTER_SUBBLOCK</a></tt> &mdash; This
beginning of a new block.</li> abbrev ID marks the beginning of a new block.</li>
<li>2 - <a href="#DEFINE_ABBREV">DEFINE_ABBREV</a> - This defines a new <li><tt>2 - <a href="#DEFINE_ABBREV">DEFINE_ABBREV</a></tt> &mdash; This defines
abbreviation.</li> a new abbreviation.</li>
<li>3 - <a href="#UNABBREV_RECORD">UNABBREV_RECORD</a> - This ID specifies the <li><tt>3 - <a href="#UNABBREV_RECORD">UNABBREV_RECORD</a></tt> &mdash; This ID
definition of an unabbreviated record.</li> specifies the definition of an unabbreviated record.</li>
</ul> </ul>
<p>Abbreviation IDs 4 and above are defined by the stream itself, and specify <p>Abbreviation IDs 4 and above are defined by the stream itself, and specify
@@ -273,14 +275,17 @@ block. In particular, each block maintains:
<li>A set of abbreviations. Abbreviations may be defined within a block, in <li>A set of abbreviations. Abbreviations may be defined within a block, in
which case they are only defined in that block (neither subblocks nor which case they are only defined in that block (neither subblocks nor
enclosing blocks see the abbreviation). Abbreviations can also be defined enclosing blocks see the abbreviation). Abbreviations can also be defined
inside a <a href="#BLOCKINFO">BLOCKINFO</a> block, in which case they are inside a <tt><a href="#BLOCKINFO">BLOCKINFO</a></tt> block, in which case
defined in all blocks that match the ID that the BLOCKINFO block is describing. they are defined in all blocks that match the ID that the BLOCKINFO block is
describing.
</li> </li>
</ol> </ol>
<p>As sub blocks are entered, these properties are saved and the new sub-block <p>
has its own set of abbreviations, and its own abbrev id width. When a sub-block As sub blocks are entered, these properties are saved and the new sub-block has
is popped, the saved values are restored.</p> its own set of abbreviations, and its own abbrev id width. When a sub-block is
popped, the saved values are restored.
</p>
</div> </div>
@@ -294,14 +299,14 @@ Encoding</a></div>
&lt;align32bits&gt;, blocklen<sub>32</sub>]</tt></p> &lt;align32bits&gt;, blocklen<sub>32</sub>]</tt></p>
<p> <p>
The ENTER_SUBBLOCK abbreviation ID specifies the start of a new block record. The <tt>ENTER_SUBBLOCK</tt> abbreviation ID specifies the start of a new block
The <tt>blockid</tt> value is encoded as a 8-bit VBR identifier, and indicates record. The <tt>blockid</tt> value is encoded as an 8-bit VBR identifier, and
the type of block being entered (which can be a <a href="#stdblocks">standard indicates the type of block being entered, which can be
block</a> or an application-specific block). The a <a href="#stdblocks">standard block</a> or an application-specific block.
<tt>newabbrevlen</tt> value is a 4-bit VBR which specifies the The <tt>newabbrevlen</tt> value is a 4-bit VBR, which specifies the abbrev id
abbrev id width for the sub-block. The <tt>blocklen</tt> is a 32-bit aligned width for the sub-block. The <tt>blocklen</tt> value is a 32-bit aligned value
value that specifies the size of the subblock, in 32-bit words. This value that specifies the size of the subblock in 32-bit words. This value allows the
allows the reader to skip over the entire block in one jump. reader to skip over the entire block in one jump.
</p> </p>
</div> </div>
@@ -315,9 +320,10 @@ Encoding</a></div>
<p><tt>[END_BLOCK, &lt;align32bits&gt;]</tt></p> <p><tt>[END_BLOCK, &lt;align32bits&gt;]</tt></p>
<p> <p>
The END_BLOCK abbreviation ID specifies the end of the current block record. The <tt>END_BLOCK</tt> abbreviation ID specifies the end of the current block
Its end is aligned to 32-bits to ensure that the size of the block is an even record. Its end is aligned to 32-bits to ensure that the size of the block is
multiple of 32-bits.</p> an even multiple of 32-bits.
</p>
</div> </div>
@@ -331,11 +337,12 @@ multiple of 32-bits.</p>
<p> <p>
Data records consist of a record code and a number of (up to) 64-bit integer Data records consist of a record code and a number of (up to) 64-bit integer
values. The interpretation of the code and values is application specific and values. The interpretation of the code and values is application specific and
there are multiple different ways to encode a record (with an unabbrev record there are multiple different ways to encode a record (with an unabbrev record or
or with an abbreviation). In the LLVM IR format, for example, there is a record with an abbreviation). In the LLVM IR format, for example, there is a record
which encodes the target triple of a module. The code is MODULE_CODE_TRIPLE, which encodes the target triple of a module. The code is
and the values of the record are the ascii codes for the characters in the <tt>MODULE_CODE_TRIPLE</tt>, and the values of the record are the ASCII codes
string.</p> for the characters in the string.
</p>
</div> </div>
@@ -348,17 +355,21 @@ Encoding</a></div>
<p><tt>[UNABBREV_RECORD, code<sub>vbr6</sub>, numops<sub>vbr6</sub>, <p><tt>[UNABBREV_RECORD, code<sub>vbr6</sub>, numops<sub>vbr6</sub>,
op0<sub>vbr6</sub>, op1<sub>vbr6</sub>, ...]</tt></p> op0<sub>vbr6</sub>, op1<sub>vbr6</sub>, ...]</tt></p>
<p>An UNABBREV_RECORD provides a default fallback encoding, which is both <p>
completely general and also extremely inefficient. It can describe an arbitrary An <tt>UNABBREV_RECORD</tt> provides a default fallback encoding, which is both
record, by emitting the code and operands as vbrs.</p> completely general and extremely inefficient. It can describe an arbitrary
record by emitting the code and operands as vbrs.
</p>
<p>For example, emitting an LLVM IR target triple as an unabbreviated record <p>
requires emitting the UNABBREV_RECORD abbrevid, a vbr6 for the For example, emitting an LLVM IR target triple as an unabbreviated record
MODULE_CODE_TRIPLE code, a vbr6 for the length of the string (which is equal to requires emitting the <tt>UNABBREV_RECORD</tt> abbrevid, a vbr6 for the
the number of operands), and a vbr6 for each character. Since there are no <tt>MODULE_CODE_TRIPLE</tt> code, a vbr6 for the length of the string, which is
letters with value less than 32, each letter would need to be emitted as at equal to the number of operands, and a vbr6 for each character. Because there
least a two-part VBR, which means that each letter would require at least 12 are no letters with values less than 32, each letter would need to be emitted as
bits. This is not an efficient encoding, but it is fully general.</p> at least a two-part VBR, which means that each letter would require at least 12
bits. This is not an efficient encoding, but it is fully general.
</p>
</div> </div>
@@ -370,13 +381,14 @@ Encoding</a></div>
<p><tt>[&lt;abbrevid&gt;, fields...]</tt></p> <p><tt>[&lt;abbrevid&gt;, fields...]</tt></p>
<p>An abbreviated record is a abbreviation id followed by a set of fields that <p>
are encoded according to the <a href="#abbreviations">abbreviation An abbreviated record is a abbreviation id followed by a set of fields that are
definition</a>. This allows records to be encoded significantly more densely encoded according to the <a href="#abbreviations">abbreviation definition</a>.
than records encoded with the <a href="#UNABBREV_RECORD">UNABBREV_RECORD</a> This allows records to be encoded significantly more densely than records
type, and allows the abbreviation types to be specified in the stream itself, encoded with the <tt><a href="#UNABBREV_RECORD">UNABBREV_RECORD</a></tt> type,
which allows the files to be completely self describing. The actual encoding and allows the abbreviation types to be specified in the stream itself, which
of abbreviations is defined below. allows the files to be completely self describing. The actual encoding of
abbreviations is defined below.
</p> </p>
</div> </div>
@@ -395,7 +407,7 @@ emitted.
</p> </p>
<p> <p>
Abbreviations can be determined dynamically per client, per file. Since the Abbreviations can be determined dynamically per client, per file. Because the
abbreviations are stored in the bitstream itself, different streams of the same abbreviations are stored in the bitstream itself, different streams of the same
format can contain different sets of abbreviations if the specific stream does format can contain different sets of abbreviations if the specific stream does
not need it. As a concrete example, LLVM IR files usually emit an abbreviation not need it. As a concrete example, LLVM IR files usually emit an abbreviation
@@ -413,33 +425,36 @@ operators, the abbreviation does not need to be emitted.
<p><tt>[DEFINE_ABBREV, numabbrevops<sub>vbr5</sub>, abbrevop0, abbrevop1, <p><tt>[DEFINE_ABBREV, numabbrevops<sub>vbr5</sub>, abbrevop0, abbrevop1,
...]</tt></p> ...]</tt></p>
<p>A DEFINE_ABBREV record adds an abbreviation to the list of currently <p>
defined abbreviations in the scope of this block. This definition only A <tt>DEFINE_ABBREV</tt> record adds an abbreviation to the list of currently
exists inside this immediate block -- it is not visible in subblocks or defined abbreviations in the scope of this block. This definition only exists
enclosing blocks. inside this immediate block &mdash; it is not visible in subblocks or enclosing
Abbreviations are implicitly assigned IDs blocks. Abbreviations are implicitly assigned IDs sequentially starting from 4
sequentially starting from 4 (the first application-defined abbreviation ID). (the first application-defined abbreviation ID). Any abbreviations defined in a
Any abbreviations defined in a BLOCKINFO record receive IDs first, in order, <tt>BLOCKINFO</tt> record receive IDs first, in order, followed by any
followed by any abbreviations defined within the block itself. abbreviations defined within the block itself. Abbreviated data records
Abbreviated data records reference this ID to indicate what abbreviation reference this ID to indicate what abbreviation they are invoking.
they are invoking.</p> </p>
<p>An abbreviation definition consists of the DEFINE_ABBREV abbrevid followed <p>
by a VBR that specifies the number of abbrev operands, then the abbrev An abbreviation definition consists of the <tt>DEFINE_ABBREV</tt> abbrevid
followed by a VBR that specifies the number of abbrev operands, then the abbrev
operands themselves. Abbreviation operands come in three forms. They all start operands themselves. Abbreviation operands come in three forms. They all start
with a single bit that indicates whether the abbrev operand is a literal operand with a single bit that indicates whether the abbrev operand is a literal operand
(when the bit is 1) or an encoding operand (when the bit is 0).</p> (when the bit is 1) or an encoding operand (when the bit is 0).
</p>
<ol> <ol>
<li>Literal operands - <tt>[1<sub>1</sub>, litvalue<sub>vbr8</sub>]</tt> - <li>Literal operands &mdash; <tt>[1<sub>1</sub>, litvalue<sub>vbr8</sub>]</tt>
Literal operands specify that the value in the result &mdash; Literal operands specify that the value in the result is always a single
is always a single specific value. This specific value is emitted as a vbr8 specific value. This specific value is emitted as a vbr8 after the bit
after the bit indicating that it is a literal operand.</li> indicating that it is a literal operand.</li>
<li>Encoding info without data - <tt>[0<sub>1</sub>, encoding<sub>3</sub>]</tt> <li>Encoding info without data &mdash; <tt>[0<sub>1</sub>,
- Operand encodings that do not have extra data are just emitted as their code. encoding<sub>3</sub>]</tt> &mdash; Operand encodings that do not have extra
data are just emitted as their code.
</li> </li>
<li>Encoding info with data - <tt>[0<sub>1</sub>, encoding<sub>3</sub>, <li>Encoding info with data &mdash; <tt>[0<sub>1</sub>, encoding<sub>3</sub>,
value<sub>vbr5</sub>]</tt> - Operand encodings that do have extra data are value<sub>vbr5</sub>]</tt> &mdash; Operand encodings that do have extra data are
emitted as their code, followed by the extra data. emitted as their code, followed by the extra data.
</li> </li>
</ol> </ol>
@@ -447,53 +462,65 @@ emitted as their code, followed by the extra data.
<p>The possible operand encodings are:</p> <p>The possible operand encodings are:</p>
<ul> <ul>
<li>1 - Fixed - The field should be emitted as a <a <li>1 &mdash; Fixed &mdash; The field should be emitted as
href="#fixedwidth">fixed-width value</a>, whose width a <a href="#fixedwidth">fixed-width value</a>, whose width is specified by
is specified by the operand's extra data.</li> the operand's extra data.</li>
<li>2 - VBR - The field should be emitted as a <a <li>2 &mdash; VBR &mdash; The field should be emitted as
href="#variablewidth">variable-width value</a>, whose width a <a href="#variablewidth">variable-width value</a>, whose width is
is specified by the operand's extra data.</li> specified by the operand's extra data.</li>
<li>3 - Array - This field is an array of values. The array operand has no <li>3 &mdash; Array &mdash; This field is an array of values. The array operand
extra data, but expects another operand to follow it which indicates the has no extra data, but expects another operand to follow it which indicates
element type of the array. When reading an array in an abbreviated record, the element type of the array. When reading an array in an abbreviated
the first integer is a vbr6 that indicates the array length, followed by record, the first integer is a vbr6 that indicates the array length,
the encoded elements of the array. An array may only occur as the last followed by the encoded elements of the array. An array may only occur as
operand of an abbreviation (except for the one final operand that gives the last operand of an abbreviation (except for the one final operand that
the array's type).</li> gives the array's type).</li>
<li>4 - Char6 - This field should be emitted as a <a href="#char6">char6-encoded <li>4 &mdash; Char6 &mdash; This field should be emitted as
value</a>. This operand type takes no extra data.</li> a <a href="#char6">char6-encoded value</a>. This operand type takes no
extra data.</li>
</ul> </ul>
<p>For example, target triples in LLVM modules are encoded as a record of the <p>
For example, target triples in LLVM modules are encoded as a record of the
form <tt>[TRIPLE, 'a', 'b', 'c', 'd']</tt>. Consider if the bitstream emitted form <tt>[TRIPLE, 'a', 'b', 'c', 'd']</tt>. Consider if the bitstream emitted
the following abbrev entry:</p> the following abbrev entry:
</p>
<ul> <div class="doc_code">
<li><tt>[0, Fixed, 4]</tt></li> <pre>
<li><tt>[0, Array]</tt></li> [0, Fixed, 4]
<li><tt>[0, Char6]</tt></li> [0, Array]
</ul> [0, Char6]
</pre>
</div>
<p>When emitting a record with this abbreviation, the above entry would be <p>
emitted as:</p> When emitting a record with this abbreviation, the above entry would be emitted
as:
</p>
<p><tt>[4<sub>abbrevwidth</sub>, 2<sub>4</sub>, 4<sub>vbr6</sub>, <div class="doc_code">
0<sub>6</sub>, 1<sub>6</sub>, 2<sub>6</sub>, 3<sub>6</sub>]</tt></p> <pre>
[4<sub>abbrevwidth</sub>, 2<sub>4</sub>, 4<sub>vbr6</sub>, 0<sub>6</sub>, 1<sub>6</sub>, 2<sub>6</sub>, 3<sub>6</sub>]
</pre>
</div>
<p>These values are:</p> <p>These values are:</p>
<ol> <ol>
<li>The first value, 4, is the abbreviation ID for this abbreviation.</li> <li>The first value, 4, is the abbreviation ID for this abbreviation.</li>
<li>The second value, 2, is the code for TRIPLE in LLVM IR files.</li> <li>The second value, 2, is the code for <tt>TRIPLE</tt> in LLVM IR files.</li>
<li>The third value, 4, is the length of the array.</li> <li>The third value, 4, is the length of the array.</li>
<li>The rest of the values are the char6 encoded values for "abcd".</li> <li>The rest of the values are the char6 encoded values
for <tt>"abcd"</tt>.</li>
</ol> </ol>
<p>With this abbreviation, the triple is emitted with only 37 bits (assuming a <p>
With this abbreviation, the triple is emitted with only 37 bits (assuming a
abbrev id width of 3). Without the abbreviation, significantly more space would abbrev id width of 3). Without the abbreviation, significantly more space would
be required to emit the target triple. Also, since the TRIPLE value is not be required to emit the target triple. Also, because the <tt>TRIPLE</tt> value
emitted as a literal in the abbreviation, the abbreviation can also be used for is not emitted as a literal in the abbreviation, the abbreviation can also be
any other string value. used for any other string value.
</p> </p>
</div> </div>
@@ -519,33 +546,38 @@ Block</a></div>
<div class="doc_text"> <div class="doc_text">
<p>The BLOCKINFO block allows the description of metadata for other blocks. The <p>
currently specified records are:</p> The <tt>BLOCKINFO</tt> block allows the description of metadata for other
blocks. The currently specified records are:
<ul> </p>
<li><tt>[SETBID (#1), blockid]</tt></li>
<li><tt>[DEFINE_ABBREV, ...]</tt></li> <div class="doc_code">
</ul> <pre>
[SETBID (#1), blockid]
[DEFINE_ABBREV, ...]
</pre>
</div>
<p> <p>
The SETBID record indicates which block ID is being described. SETBID The <tt>SETBID</tt> record indicates which block ID is being
records can occur multiple times throughout the block to change which described. <tt>SETBID</tt> records can occur multiple times throughout the
block ID is being described. There must be a SETBID record prior to block to change which block ID is being described. There must be
any other records. a <tt>SETBID</tt> record prior to any other records.
</p> </p>
<p> <p>
Standard DEFINE_ABBREV records can occur inside BLOCKINFO blocks, but unlike Standard <tt>DEFINE_ABBREV</tt> records can occur inside <tt>BLOCKINFO</tt>
their occurrence in normal blocks, the abbreviation is defined for blocks blocks, but unlike their occurrence in normal blocks, the abbreviation is
matching the block ID we are describing, <i>not</i> the BLOCKINFO block itself. defined for blocks matching the block ID we are describing, <i>not</i> the
The abbreviations defined in BLOCKINFO blocks receive abbreviation ids <tt>BLOCKINFO</tt> block itself. The abbreviations defined
as described in <a href="#DEFINE_ABBREV">DEFINE_ABBREV</a>. in <tt>BLOCKINFO</tt> blocks receive abbreviation IDs as described
in <tt><a href="#DEFINE_ABBREV">DEFINE_ABBREV</a></tt>.
</p> </p>
<p> <p>
Note that although the data in BLOCKINFO blocks is described as "metadata," the Note that although the data in <tt>BLOCKINFO</tt> blocks is described as
abbreviations they contain are essential for parsing records from the "metadata," the abbreviations they contain are essential for parsing records
corresponding blocks. It is not safe to skip them. from the corresponding blocks. It is not safe to skip them.
</p> </p>
</div> </div>
@@ -556,24 +588,29 @@ corresponding blocks. It is not safe to skip them.
<div class="doc_text"> <div class="doc_text">
<p>Bitcode files for LLVM IR may optionally be wrapped in a simple wrapper <p>
Bitcode files for LLVM IR may optionally be wrapped in a simple wrapper
structure. This structure contains a simple header that indicates the offset structure. This structure contains a simple header that indicates the offset
and size of the embedded BC file. This allows additional information to be and size of the embedded BC file. This allows additional information to be
stored alongside the BC file. The structure of this file header is: stored alongside the BC file. The structure of this file header is:
</p> </p>
<p> <div class="doc_code">
<tt>[Magic<sub>32</sub>, Version<sub>32</sub>, Offset<sub>32</sub>, <pre>
Size<sub>32</sub>, CPUType<sub>32</sub>]</tt></p> [Magic<sub>32</sub>, Version<sub>32</sub>, Offset<sub>32</sub>, Size<sub>32</sub>, CPUType<sub>32</sub>]
</pre>
</div>
<p>Each of the fields are 32-bit fields stored in little endian form (as with <p>
Each of the fields are 32-bit fields stored in little endian form (as with
the rest of the bitcode file fields). The Magic number is always the rest of the bitcode file fields). The Magic number is always
<tt>0x0B17C0DE</tt> and the version is currently always <tt>0</tt>. The Offset <tt>0x0B17C0DE</tt> and the version is currently always <tt>0</tt>. The Offset
field is the offset in bytes to the start of the bitcode stream in the file, and field is the offset in bytes to the start of the bitcode stream in the file, and
the Size field is a size in bytes of the stream. CPUType is a target-specific the Size field is a size in bytes of the stream. CPUType is a target-specific
value that can be used to encode the CPU of the target. value that can be used to encode the CPU of the target.
</div> </p>
</div>
<!-- *********************************************************************** --> <!-- *********************************************************************** -->
<div class="doc_section"> <a name="llvmir">LLVM IR Encoding</a></div> <div class="doc_section"> <a name="llvmir">LLVM IR Encoding</a></div>
@@ -581,12 +618,14 @@ value that can be used to encode the CPU of the target.
<div class="doc_text"> <div class="doc_text">
<p>LLVM IR is encoded into a bitstream by defining blocks and records. It uses <p>
LLVM IR is encoded into a bitstream by defining blocks and records. It uses
blocks for things like constant pools, functions, symbol tables, etc. It uses blocks for things like constant pools, functions, symbol tables, etc. It uses
records for things like instructions, global variable descriptors, type records for things like instructions, global variable descriptors, type
descriptions, etc. This document does not describe the set of abbreviations descriptions, etc. This document does not describe the set of abbreviations
that the writer uses, as these are fully self-described in the file, and the that the writer uses, as these are fully self-described in the file, and the
reader is not allowed to build in any knowledge of this.</p> reader is not allowed to build in any knowledge of this.
</p>
</div> </div>
@@ -603,9 +642,16 @@ reader is not allowed to build in any knowledge of this.</p>
The magic number for LLVM IR files is: The magic number for LLVM IR files is:
</p> </p>
<p><tt>[0x0<sub>4</sub>, 0xC<sub>4</sub>, 0xE<sub>4</sub>, 0xD<sub>4</sub>]</tt></p> <div class="doc_code">
<pre>
[0x0<sub>4</sub>, 0xC<sub>4</sub>, 0xE<sub>4</sub>, 0xD<sub>4</sub>]
</pre>
</div>
<p>When combined with the bitcode magic number and viewed as bytes, this is "BC 0xC0DE".</p> <p>
When combined with the bitcode magic number and viewed as bytes, this is
<tt>"BC&nbsp;0xC0DE"</tt>.
</p>
</div> </div>
@@ -618,9 +664,12 @@ The magic number for LLVM IR files is:
<a href="#variablewidth">Variable Width Integers</a> are an efficient way to <a href="#variablewidth">Variable Width Integers</a> are an efficient way to
encode arbitrary sized unsigned values, but is an extremely inefficient way to encode arbitrary sized unsigned values, but is an extremely inefficient way to
encode signed values (as signed values are otherwise treated as maximally large encode signed values (as signed values are otherwise treated as maximally large
unsigned values).</p> unsigned values).
</p>
<p>As such, signed vbr values of a specific width are emitted as follows:</p> <p>
As such, signed vbr values of a specific width are emitted as follows:
</p>
<ul> <ul>
<li>Positive values are emitted as vbrs of the specified width, but with their <li>Positive values are emitted as vbrs of the specified width, but with their
@@ -629,8 +678,10 @@ unsigned values).</p>
value is shifted left by one, and the low bit is set.</li> value is shifted left by one, and the low bit is set.</li>
</ul> </ul>
<p>With this encoding, small positive and small negative values can both be <p>
emitted efficiently.</p> With this encoding, small positive and small negative values can both be emitted
efficiently.
</p>
</div> </div>
@@ -645,15 +696,21 @@ LLVM IR is defined with the following blocks:
</p> </p>
<ul> <ul>
<li>8 - MODULE_BLOCK - This is the top-level block that contains the <li>8 &mdash; <tt>MODULE_BLOCK</tt> &mdash; This is the top-level block that
entire module, and describes a variety of per-module information.</li> contains the entire module, and describes a variety of per-module
<li>9 - PARAMATTR_BLOCK - This enumerates the parameter attributes.</li> information.</li>
<li>10 - TYPE_BLOCK - This describes all of the types in the module.</li> <li>9 &mdash; <tt>PARAMATTR_BLOCK</tt> &mdash; This enumerates the parameter
<li>11 - CONSTANTS_BLOCK - This describes constants for a module or attributes.</li>
function.</li> <li>10 &mdash; <tt>TYPE_BLOCK</tt> &mdash; This describes all of the types in
<li>12 - FUNCTION_BLOCK - This describes a function body.</li> the module.</li>
<li>13 - TYPE_SYMTAB_BLOCK - This describes the type symbol table.</li> <li>11 &mdash; <tt>CONSTANTS_BLOCK</tt> &mdash; This describes constants for a
<li>14 - VALUE_SYMTAB_BLOCK - This describes a value symbol table.</li> module or function.</li>
<li>12 &mdash; <tt>FUNCTION_BLOCK</tt> &mdash; This describes a function
body.</li>
<li>13 &mdash; <tt>TYPE_SYMTAB_BLOCK</tt> &mdash; This describes the type symbol
table.</li>
<li>14 &mdash; <tt>VALUE_SYMTAB_BLOCK</tt> &mdash; This describes a value symbol
table.</li>
</ul> </ul>
</div> </div>